A wireless communication network may include a number of base stations that can support communication for a number of user equipments (UEs). In recent years, the carrier frequencies at which base stations and UEs communicate have continued to increase and include larger bandwidths. To take advantage of these higher frequencies, more antennas in the same physical space have been used. For these higher frequency bands to be useful and approximate the same coverage radius as prior technologies (such as 2G, 3G, or 4G), however, more beam forming gain (and more accurate) is becoming necessary.
Further, conventional systems employ various types of reference signals, with varying fixed structures, to provide sufficient measurements and estimations for adaptive multi-antenna operation in uplink and/or downlink directions. For example, a channel state information reference signal (CSI-RS) may be used on a downlink from the base station to aid the base station in beam form determination, an uplink demodulation reference signal (DM-RS) specific to each UE may be used to estimate channel information for the uplink specifically, and each UE may use a sounding reference signal (SRS) on the uplink to aid in scheduling (e.g., determining which frequency bands are good or bad for data). There is no single signal that is able to achieve all of above functionality for UEs.
Reciprocity describes the ability for a station to use information (such as a multipath delay profile) from one channel (e.g., the uplink) in making determinations regarding another channel (e.g., the downlink). Reciprocity has not been available for cellular networks because current approaches require reference signals specific for particular antennas, such as CSI-RS in the long term evolution (LTE) context. Further, CSI-RS and other types of signals do not scale well, which is becoming an ever-increasing issue as the demand for mobile broadband continues to increase.